Paper 3  using mixture of grit and mature compost as bulking agent- 15 jan 2012
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Paper 3 using mixture of grit and mature compost as bulking agent- 15 jan 2012

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Co-composting of primary sewage sludge with matured compost, together with grit and sand ...

Co-composting of primary sewage sludge with matured compost, together with grit and sand
was carried out to solve the problem of grit and sand disposal, this technique improved the
sludge composting efficiency and the final compost quality

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Paper 3 using mixture of grit and mature compost as bulking agent- 15 jan 2012 Document Transcript

  • 1. USING MIXTURE OF GRIT AND MATURE COMPOST AS BULKING AGENT: ITS EFFECT ON COMPOSTING EFFICIENCY AND COMPOST QUALITY. *Dr. Helalley A.H. Helalley 1, Chem. Hussein M. Elashqar 2, Dr.Samaa M.Z. Abdel Aziz 3 1 Chief of Industrial Drainage, Sludge and Reuse sector. 2 3 General Manager of Sludge and Reuse. Manager of Industrial Wastewater Research Dept., Alexandria Sanitary Drainage Company, Alexandria, Egypt Keywords Sewage grit, sewage sludge, windrow composting, co-composting. ABSTRACT Primary wastewater treatment plants in Alexandria produce large amounts of Grit and sand as one of the major solid wastes arising from the preliminary treatment stage, which represents a problem in disposal of these large quantities which are around 811 m3/month, (27 m3/day). On the other hand, one of the main sludge composting management problems is to provide the bulking agents with affordable costs. Co-composting of primary sewage sludge with matured compost, together with grit and sand was carried out to solve the problem of grit and sand disposal, this technique improved the sludge composting efficiency and the final compost quality. Dewatered primary sludge was mixed with matured compost and grit and sand as a bulking agent at 9:2:1 (v/v), and the mixtures were composted for 60 days. Addition of grit and sand raised slightly the inorganic portion of the sludge compost, and rose significantly the temperature in the first composting stage, therefore significantly increased the decomposition activity due to the facilitation of homogenicity of the mixture which resulted in high mixture porosity which improved air exchange within the mixture. The numbers of microbial pathogens were significantly decreased to the safe permitted limits as a result of the raise in temperature, thus produced a final safe product. This technique not only improved the composting operation in terms of temperature, moisture content, mixture porosity, oxygen content (up to 5%). But also reduce the cost of composting operation and solve the problem of grit and sand disposal. 1/13
  • 2. 1. INTRODUCTION: Sewage grit and sludge are inevitable by-products of wastewater treatment processes. Sewer grit is collected by traditional removal at wastewater treatment works. Its production is highly variable (0.5 to 2.0 t/year per 1000 population) depending on the catchment area (higher grit production in coastal or sandy areas), sewer type (more from combined sewers through road run-off than separate sewers), and weather conditions (grit deposited in the sewer during dry weather is washed through during storm events). Grit quality has wide variations in moisture content (7.4% to 75%) and organic content (30 – 65% total organic carbon). Sewage sludge is produced by sedimentation, both before and after wastewater biotreatment. The upgrading and expansion of wastewater treatment plants have greatly increased the volume of sludge generated. (Yongjie and Yangsheng, 2005, Lewin, et.al., 2011) Quantitative and qualitative composition of the sewage sludge is very complicated. It is rich in organic matter, nitrogen, phosphorus, calcium, magnesium, sulphur and other microelements necessary for plants and soil fauna to live. So it is characterized by the large manurial and soil-forming value. Except the indispensable elements to live, sludge can contain toxic compounds (heavy metals, pesticides) and pathogenic organisms (bacteria, eggs of parasites) (Kosobucki, et.al., 2000). The handling of sewage sludge is one of the most significant challenges in wastewater management. In many countries, sewage sludge is a serious problem due to its high treatment costs and the risks to environment and human health. Although, the volume of the produced sewage sludge represents only 1 % to 2% of the treated wastewater volume, its management costs are usually ranging from 20% to 60% of the total operating costs of the wastewater treatment plant (Marcos and Carlos, 2005). Due to the currently low capacities of wastewater treatment prevailing in many developing countries, a future increase in the number and capacities of wastewater treatment plants can be expected. As a consequence, the amount of produced sewage sludge is also expected to increase (Zaini and Mogens, 2006). These aspects show that, sewage sludge management is an increasing matter of concern in many countries due to the fast increases in sludge production, which increases the resulting environmental threats accordingly (Murphy, et.al., 2004). The beneficial use of sewage sludge in most of the developing countries as a soil conditioner or for land application can be considered as a good option. Especially, the land degradation problems and insufficient food production as well as the financial problems are considered (Ghazy, et.al., 2009). Grit consists mainly of mineral matter such as sand, gravel, glass and plastics. Owing to this high proportion of sand and gravel-sized inorganic material, sewer grit has been used in several recycling applications (Lewin, et.al., 2011). Untreated grit has been used as top cover/ infill for pipe trenches within the cartilage of wastewater treatment works during construction projects. Certain soils, particularly heavy clay soils, can benefit from the addition of grit materials to aid in drainage, to help break-up those soils and to improve compaction properties. It may be used in horticulture and agriculture. Also, grit is used as a base material for soil manufacture. Grit has also been successfully trialled as an input material for the cement industry as an alternative source of silica rich material (Lewin, et.al., 2011). 2/13
  • 3. Under aerobic conditions and in admixture with other waste, the organics which are present in sewer grit are biologically decomposed. The production of heat further sanitises the input material. In addition to sanitisation, the composted product is stabilized and becomes an important source of nutrients and humic substances that can be applied to land (Lewin, et.al., 2011). With higher grit disposal costs and a legislative requirement to “reduce, reuse and recycle”, there is a strong incentive for sewer grit recycling opportunities. This prioritizes waste prevention and recycling ahead of disposal (Lewin, et.al., 2011). Sewage sludge composting is being increasingly considered by many municipalities throughout the world because it has several advantages over other disposal strategies. Additionally, the application of composts to agricultural soils has many advantages, which include providing a whole array of nutrients to the soil, decreasing soil acidification, preventing soil erosion, increasing beneficial soil organisms, reducing the need for fertilizers and pesticides, improving soil physical and biological properties, and helping keep organic wastes out of landfills. All these effects and probably also additional ones (e.g. suppression of pathogenic microorganisms) are advantageous for plant health (Yongjie and Yangsheng, 2005). Primary wastewater treatment plants in Alexandria produce large amounts of Grit and sand as one of the major solid wastes arising from the preliminary treatment stage, which represents a problem in disposal. The quantities of grit which received at site 9N are around 811 m3/month, (27 m3/day). On the other hand, one of the main sludge composting management problems is to provide the bulking agents with affordable costs. Co-composting of primary sewage sludge with matured compost, together with grit was carried out to solve the problem of grit disposal; and testing this technique in improving the sludge composting efficiency and the final compost quality. 2. MATERIALS AND METHODS 2.1 Sewage Sludge The sewage sludge used in this study was raw dewatered municipal sewage sludge received at the landfill composting facility (site 9N) from the Mechanical Dewatering Facility (MDF) located at the West Treatment Plant in west of Alexandria (Elkabary). MDF receives all sludge resulting from primary treatment of sewage water at East and West Treatment Plants in Alexandria and small quantities from new secondary treatment plants. This raw sludge was mechanically dewatered by belt filter press to total solids of about 30%. 2.2 Sewage Grit The grit used in this study was received at site 9N from all treatment plants in Alexandria. The average of moisture content range of grit was 18-25% and the average of organic matter content range was 20-30%. 2.3 Composting Process The composting process was done at the composting facility (site 9N) of Alexandria Sanitary Drainage Company (ASDCO). It is located approximately 40 km west of Alexandria. Windrow-composting method was used throughout this study. The site 9N traditional composting process was done using a mixture of raw dewatered sewage sludge 3/13
  • 4. with mature compost (DS/MC) with a ratio of 3:1 (v/v) respectively. Five windrows all over the year were established to examine the effect of using a mixture of mature compost with grit on the composting process and the quality of compost produced. Co-composting of primary sewage sludge with matured compost, together with grit (DS/MC/G) was carried out to solve the problem of grit disposal; and to examine if this technique will effect on the sludge composting efficiency and the final compost quality. Dewatered primary sludge was mixed with matured compost and grit as a bulking agent at 9:2:1 (v/v) respectively. Both the (DS/MC) and the (DS/MC/G) mixtures were composted for 60 days with turning mechanically by using turning machine and left for another one month without turning for curing. The dimensions of each windrow were 4.2 m in width, 250 m in length, and 1.5 m in height in the triangular shape. The mixtures were mixed by turning once a day for three consecutive days and after that they were turned every 7-10 days for two months (fermentation period) and after that they were stored for another one month without turning as a curing period. The composting process consisted of two periods, the fermentation period (two months) and the maturation period (one month) without turning. 2.4 Sampling Procedure Samples were taken weekly from each pile of compost. Each composite sample was taken from ten places at random at a depth of 70- 80 cm and mixed together. Samples were transferred aseptically to the laboratory in a cold box and analyzed chemically and microbiologically. 2.5 Laboratory Analysis 2.5.1 Physical analysis Temperature was monitored near the centre of the pile with a metal probe thermometer (Poincelot and Day, 1973). It was checked every week at five points along the pile. The colour was assessed visually, while the odour was sensed by smelling (Khalil, 1996). The colour and odour were tested by three persons. 2.5.2 Chemical analysis Samples were oven-dried (60-70 °C), ground in a porcelain mortar and then by a hammer mill. The ground samples were stored in dry, airtight containers until use. pH and Electric conductivity were determined by shaking 5.0 g compost in 50.0 ml distilled water (1:10, w/v) for 30 min, then pH was measured by a pH meter and electric conductivity meter (Albonetti and Massari, 1979). Moisture content and dry weight were determined after drying the sample at 105 °C. Ash was determined after drying the sample at 105 °C and ashing at 550 °C, in a muffle furnace for about 3 h (WHO, 1978, APHA, 1998). Percentages of organic matter were estimated as follows: Organic matter (%) = 100 - ash (%)(WHO, 1978, Okalebo, et.al., 1993) Total nitrogen was determined by the Kjeldahl method (WHO, 1978). Phosphorus was determined by spectrophotometer at 470 nm, while potassium and heavy metals was determined by Atomic Absorption Spectroscopy (WHO, 1978). 4/13
  • 5. 2.5.3 Detection of pathogenic bacteria Multiple tube fermentation tests were used for fecal coliforms according to the method of APHA (2005). Salmonella was determined as described by APHA (2005) and (ISO 6579, 1993). 2.6 Statistical Analysis Standard analysis of variance (ANOVA: two-factor with replication) was used. Analysis of variance was computed using the Microsoft Excel software. Differences of means were based on the least significant difference (LSD) at P= 0.05. 3. RESULTS AND DISCUSSION: Physical and chemical changes were examined periodically in this study together with the heavy metals content and the pathogenic microorganisms. 3.1 Physical changes: 3.1.1 Temperature: Temperature changes that occurred in the different windrows are shown in Figure (1). The temperature of raw dewatered sewage sludge before mixing was about 29°C and after mixing the temperature began to rise to 44°C in average at the third day of composting. During the composting process, the temperatures of the windrows increased rapidly after mixing where it reached about 52.3 and 53.4°C in DS/MC and DS/MC/G respectively after 7 days. The maximum temperatures during the fermentation period of the DS/MC reached 68.4 °C after 8 weeks, while for the DS/MC/G it reached 70.4 °C after 5 weeks. Afterwards the temperatures decreased gradually during the curing period as it reached an average temperature of 51.6 and 51.4 °C, respectively. Although in the case of DS/MC it is noticed that the temperature increased gradually and reach the maximum at week 8 but in the case of DS/MC/G it was observed that the temperature increased rapidly in the first 3 weeks and reach maximum at week 5. This mainly is due to the improving of the efficiency of mixing and aeration which provide good ventilation conditions inside the composting windrow as a result of grit and raw sludge mixing. Also, the warming up in the first stage of DS/MC/G was faster as related to high porosity of the mixture which led to better aeration conditions thus improving the activity of the aerobic microorganisms which is responsible for the activity increase of composting process and temperature elevation. The temperature in both cases began to decrease below 55°C at the end of composting process. It was mentioned that observing windrow temperature is the best way to monitor the composting process (Diaz, et.al., 1993). It was also demonstrated that the single best way to monitor the composting process is by observing temperature at points along the windrow (Kuhlman, 1985). It was also mentioned that compost is matured enough when its temperature remains more or less constant and does not vary with the turning of the material (Iacoboni, 1984). Therefore, this parameter may be considered as a good indicator for the end of the 5/13
  • 6. biooxidative phase in which the compost achieves some degree of maturity (Jiménez, and Garcia, 1989). In the present study, the mesophilic condition prevailed during the first three days, and then the thermophilic stage dominated all over the composting process. Maturation period, characterized by high temperature, began as temperature cooled down slowly but it was still above 55 °C. These results are comparable with a study which stated that maturation piles when left unturned for 4-10 weeks maturation, the temperatures remained at 65-75 °C (Purcell, and Stentiford, 2001). According to Fogarty and Tuovinen (1991) aeration during composting has multiple functions: 1) it supplies O2 to support aerobic metabolism (oxygenase functions and aerobic respiration), 2) it controls the temperature, and 3) it removes excess moisture as well as CO2 and other gasses. Moreover, it was mentioned that the overall goal of the aeration is to maintain compost temperature in the range of 50- 55 °C to obtain efficient thermophilic decomposition of organic wastes and pathogen destruction (Jeris, and Regan, 1973, Mckinley, and Vestal, 1984, Schulze, 1962). 1.2 Odour Odour was recorded during the composting processes. It was found that the unpleasant odour of composting materials decreased with time. Odour increased immediately after turning, but within a short time (30-45 min) it became as before turning. The unpleasant odour decreased after 40-50 days of composting but did not disappear completely. At the end of the composting process, the odour of both windrows were low and the odour of composts after storage for another one month were similar to the odour of earth especially at low levels of moisture contents (less than 10%). These results are in agreement with other studies which mentioned that composting is at the end when unpleasant odours disappear and changed to an earthy odour (Diaz, et.al., 1993, Jiménez, and Garcia, 1989). 1.3 Colour During the composting process, a gradual change in colour from black to brownish black took place and this gave indication of the maturity progress. Morphologically, the composts of all windrows were nearly homogenous with fine grain powder and had a black-brown colour or greyish black at the end of process. It is noticed that the compost of DS/MC/G was more friable than DS/MC compost. These results are in agreement with other studies which mentioned that by the time the process is finished it has become a dark grey to brown in colour or brownish-black (Diaz, et.al., 1993, Gotaas, 1956). 6/13
  • 7. 80 o Temperature ( C) 70 60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Composting time (Weeks) DS/MC DS/MC/G Figure (1): Changes in temperature during the composting and co-composting of sewage sludge and sewage grit at site 9n. - Values are means of three replicates±standard deviations. - DS/M C: Windrow composting of dewatered sludge and matured compost. - DS/MC/G: Windrow co-composting of dewatered sludge and matured compost with grit. 2. Chemical changes: The chemical parameters measured in the final composts after the composting and cocomposting processes were organic matter (OM), nitrogen (N), Phosphorus (p), Potassium (p), pH, electric conductivity and heavy metals. Results of chemical changes in all parameters measured are shown in Figures (2-6). The final results of composting and co-composting obtained showed that all chemical parameters results of DS/MC/G decreased than DS/MC except for pH, P and K which increased slightly. The pH of DS/MC compost was 6.9 and DS/MC/G compost was 7.15. Both results are neutral and indicate good maturity. The OM content of DS/MC/G compost less than DS/MC compost and it was 31.35% and 39.5% respectively. These results indicate that the addition of grit in this study increased the porosity of the windrows, thus improving the aeration process. The good aerobic conditions are recommended to maintain a rapid and complete breakdown of readily decomposable organic compounds. Also, the organic content of sewage grit is low and so decreased the OM content when co-composted with sludge. Also, the N content of DS/MC/G compost was less than DS/MC compost and it was 1.6% and 2.6% respectively. The P and K content of both DS/MC/G compost and DS/MC compost appear to be nearly the same. The P content was 0.6% and 0.5% for DS/MC/G compost and DS/MC compost, respectively. Also, the results indicate that the K content was 0.16% and 0.1% for DS/MC/G compost and DS/MC compost, respectively. The N, P and K contents in both composts are good percentages and adequate for using the compost as soil conditioner and fertilizer. Electric conductivity measured in both composts is illustrated in Figure (5). The 7/13
  • 8. electric conductivity of DS/MC/G compost was 2.63 and of DS/MC compost was 3.5. The decrease in electric conductivity of DS/MC/G compost is related to the addition of grit to sewage sludge. The sewage grit mainly content is sand which has low electric conductivity. The results are in agreement with other studies which stated that from fermentation studies it is known that aerobic conditions prompt rapid and complete degradation of organic materials by microorganisms. If anaerobic conditions prevail, slow degradation takes place accompanied by accumulation of intermediary products, which give an offensive odour. Therefore, aerobic conditions are recommended to maintain a rapid and complete breakdown of readily decomposable organic compounds (Jeris, and Regan, 1973, Jann, et.al., 1959). It is of prime importance to stabilize the organic waste rapidly. It can be concluded that frequent turning can achieve this (Jann, et.al., 1959). Inbar et al., (1990) mentioned that about 50% of the organic matter is metabolized to CO2 and H2O during the composting of separated cattle manure. Also, other studies stated that maturation phase produced further reduction in moisture content to 30- 40% and volatile solids to 40% (Purcell, and Stentiford, 2001). The curing and any subsequent storage can be considered as an extension of the composting process and are associated with elevated temperatures (Willson, et.al., 1980). Also, it was mentioned that, when the composted sludge has reached at least less than 40% moisture and the volatile solids has been reduced to below 40%, the material is dry and stable enough to be used as a fertilizer (Iacoboni, et.al., 1984). pH 7.40 7.30 7.20 7.10 7.00 6.90 6.80 6.70 6.60 6.50 6.40 6.30 Sample (1) Sample (2) Sample (3) DS/MC Sample (4) Sample (5) average DS/MC/G Figure (2): pH changes in the final composts from composting and co-composting at site 9N. Organic Matter Content 50 Percent % 45 40 35 30 25 20 15 10 5 0 Sample (1) Sample (2) Sample (3) Sample (4) Sample (5) DS/MC average DS/MC/G Figure (3): Organic Matter content in the final composts from composting and co-composting at site 9N. 8/13
  • 9. N,P and K content 3.0 Percent (%) 2.5 2.0 1.5 1.0 0.5 0.0 DS/MC DS/MC/G N P K Figure (4): N,P and K content in the final composts from composting and co-composting at site 9N. Ele ctric Conductivity E.C 4.5 4 3.5 d /m s 3 2.5 2 1.5 1 0.5 0 Sa mple (1) Sa mple (2) Sa mple (3) DS/MC Sa mple (4) Sa mple (5) average DS/MC/G Figure (5): Electric Conductivity changes in the final composts from composting and co-composting. 3. Heavy metals content As illustrated in Figure (6), the heavy metals content in the final composts of both composting and co-composting of swage sludge and sewage grit are lower than the permissible levels of Egyptian Sludge Regulation (Directive 254/2003)(Egyptian Code, 2005) concerning processing and safe use of sludge in agricultural purposes. Also, the addition of grit to sewage sludge led to decrease the all heavy metals content detected in case of DS/MC/G compost than DS/MC compost except for lead metal. The slightly increase of Pb in case of DS/MC/G compost than DS/MC compost result from the addition of grit which contain high content of Pb and Cu than other metals as shown in Table (1). The results obtained showed that the average of Zn content in the final composts was 1143.9 and 807.26 mg/kg in case of DS/MC and DS/MC/G, respectively, the Cu content was 252.6 and 209.28 mg/kg in case of DS/MC and DS/MC/G, respectively, the Ni content was 32.4 and 26.37 mg/kg in case of DS/MC and DS/MC/G, respectively, the Cd content was 1.3 and 0.74 mg/kg in case of DS/MC and DS/MC/G, respectively, the Pb content was 245.1 and 261.3 mg/kg in case of DS/MC and DS/MC/G, respectively, and the Cr content was 67.0 and 27.54 mg/kg in case of DS/MC and DS/MC/G, respectively. As mentioned above, the results indicated that the mixing of grit which contains low levels of heavy metals as shown in Table (1) with sewage sludge is the reason for decrease the heavy metals content in DS/MC/G compost than DS/MC compost. 9/13
  • 10. Table (1): Heavy metals content of raw sewage grit before composting Metals (mg/kg) Sample 1 Sample 2 Zn 0.072 0.0395 Cu 0.1771 0.2006 Ni 0.0297 0.0249 Cd Pb 0.0027 0.0038 0.218 0.224 Cr 0.013 0.0187 Average of heavy metals content 1400 1200 (mg/kg) 1000 800 600 400 200 0 Zn Cu Ni DS/MC Cd Pb Cr DS/MC/G Figures (6): The heavy metals content in the final composts from composting and co-composting. 4. Detection of pathogens In respect to pathogen and parasite destruction, the relative elimination efficiencies of the composting process were evaluated on the basis of existence of indicator microorganisms (fecal coliforms), enteric pathogenic bacteria (Salmonella spp.) and Ascaris ova. The counts of fecal coliforms during the composting and co-composting of sewage sludge and swage grit are shown in Table (2) and (3). The counts of fecal coliforms in raw sewage sludge and raw grit were 7x109 and 1.7x105 MPN/g, respectively, and with the advance of composting and co-composting processes, the counts became zero in both DS/MC compost and DS/MC/G compost. The results of fecal coliform counts had lower number than the permissible levels of fecal coliforms in the Egyptian Sludge Regulation (Decree 254/2003) (Egyptian Code, 2005), which specifies that the fecal coliforms MPN should be less than 1000 cells/g dry solids. In respect to Salmonella spp., the results indicated that the count in raw sewage sludge and raw grit were 2.1x104 and 1.8x102 MPN/g, respectively, and at the end of composting and co-composting processes, the counts became <2 in both DS/MC compost and DS/MC/G compost. It is noticed also that all results were within the permissible levels of Salmonellae specified in the Egyptian Sludge Regulation (Decree 254/2003)( Egyptian Code, 2005) 10/13
  • 11. concerning processing and safe use of sludge in agricultural purposes, which specify that the Salmonella MPN count should be less than 3 cells/100 ml at a sludge concentration of 4% dry solids. Ascaris ova count was positive in both raw sewage sludge and raw sewage grit which disappeared after composting and co-composting processes and became negative in both DS/MC compost and DS/MC/G compost. The results of Ascaris ova count indicate that they had lower number than the permissible levels of Ascaris ova in the Egyptian Sludge Regulation (Decree 254/2003)( Egyptian Code, 2005), which specifies that the Ascaris ova MPN should be 1 cells/100 ml at a sludge concentration of 5% dry solids. To discuss the results of the present study it should be mentioned that total and fecal coliforms, Salmonella, Ascaris counts were selected because of their value as indicator organisms, and because they are enteric pathogens known to be present in relatively high numbers (54,122). These results agree with those reported in other study, which stated that coliforms are more resistant to inactivation than Salmonella spp. and thus are good indicator organisms (124). There is extensive data indicating that the densities of fecal coliforms are good indicators of the effectiveness of the composting process in destroying enteric pathogens such as Salmonella spp. Studies at the Los Angeles county facility determined that the fecal coliforms concentrations of less than 1000 MPN/g indicated a high probability of destruction of bacteria and parasitic and viral pathogens (146). Generally, the results of all final composts in this study were negative for the tested pathogens and parasites. This meant that these composts are safe for handling as previously reported that when an intensive control program for composting process is carried out with regard to viruses, bacteria and parasites, the hygienic quality becomes satisfactory (13). Table (2): Typical pathogens count in raw sewage sludge and sewage grit Pathogens Raw Sewage Sludge Sewage Grit Count/100/ ml Count/100 ml 7x109 2.1x104 +ve Fecal Coliform Bacteria Salmonella Ascaris ova 1.7x105 1.8x102 +ve Table (3): Typical pathogens count after the composting and co-composting. . DS/MC DS/MC/G Count/100/ ml Count/100 ml -ve Fecal Coliform Bacteria -ve <2 Salmonella <2 -ve Ascaris ova -ve Pathogens 11/13
  • 12. 4. CONCLUSIONS: 1- Co-composting of sewage sludge with sewage grit is an effective and safe method for treatment of grit and disposal method buy reuse. 2- Addition of grit to sewage sludge as bulking agent during composting process increases the porosity and improves aeration inside the windrows that made composting process faster in time. 3- The temperature during the co-composting of sewage sludge and sewage grit was high enough and it was within the effective range for pathogen and parasite destruction. 4- The compost produced from co-composting of sewage sludge and sewage grit is free of pathogens and safe enough for using as soil conditioner and fertilizer for landscape and ornamental plants. 5- The lower heavy metals content in grit that mixed with sewage sludge in this study decreased the heavy metals content in compost produced. 5. REFERENCES: Albonetti, S.G. and Massari, G. (1979). Microbiological aspects of a municipal waste composting system. European J. Appl. Microbiol. Biotechnol., 7: 91-98. Alexander, R. (1990). Expanding compost markets. BioCycle, 31(8): 54-59. APHA (2005). Standard Methods for the Examination of Water and Wastewater. 21st Edition. Bertoldi, M., Civilini, M. and Comi, G. (1990). MSW compost standards in the European community. BioCycle, 31(8): 60-62. Boutillot, G. (1999). Evaluation of sewage sludge composting in Alexandria (Egypt) to ensure a quality assured product for use in agriculture. Engineering thesis, Institute of Irrigation and Developed Studies, University of Southampton, Water Research Centre, Medmenhan, UK. Diaz, L.F., Savage, G.M., Eggerth, L.L. and Golueke, C.G. (1993). Composting and Recycling Municipal Solid Waste. Calrecovery Inc., Hercules, California, U.S.A. Egyptian Code ECP 501-2005, (2005). “Egyptian standards for use of treated wastewater in agriculture”. Fogarty, A.M. and Tuovinen, O.H. (1991). Microbiological degradation of pesticides in yard waste composting. Microbiol. Reviews, 55(2): 225-233. Furhacker, M. and Haberl, R. (1995). Composting of sewage sludge in a rotating vessel. Water Sci. Tech., 32(11): 121-125. Ghazy, M., Dockhorn, T. and Dichtl, N., (2009). “Sewage Sludge Management in Egypt: Current Status and Perspectives towards a Sustainable Agricultural Use” World Academy of Science, Engineering and Technology, vol. 57, 299-307. Hay, C.J. (1996). Pathogen destruction and biosolids composting, Monitoring and control. BioCycle, 37(6): 67-76. Iacoboni, M.D. (1984). Windrow and static pile composting of municipal sewage sludge. Los Angeles County Sanitation Districts Whitter, CA, Prepared for municipal environmental research lab., Cincinnati, OH. 12/13
  • 13. Iacoboni, M.D., Livingston, R.J., and Lebrun, J.T. (1984). Windrow and Static Pile Composting of Municipal Sewage Sludge. EPA-600/2-84-122. Inbar, Y., Chen, Y., Hadar, Y. and Hoitink, H.A.J. (1990). New approaches to compost maturity. BioCycle, 31 (12): 4-69. Jeris, J.S. and Regan, R.W. (1973). Controlling environmental parameters for optimum composting Part II: Moisture, free air space and recycle. Compost Sci., 14 (2): 8-15. Jeris, J.S. and Regan, R.W. (1973). Controlling environmental parameters for optimum composting. Part 1: Experimental procedures and temperature. Compost Sci., 14(1): 1015. Khalil, A.I. (1996). Composting and the Utilization of Organic Wastes: An Environmental Study. PhD. Thesis, Institute of Graduate Studies and Research, Alex. University, Alexandria, Egypt. Kosobucki, P., Chmarzyński, A. and Buszewski, B., (2000). Sewage Sludge Composting. Polish Journal of Environmental Studies Vol. 9, No. 4: 243-248. Marcos v. S., and Carlos A. C., (2005). “Biological wastewater treatment in warm climate regions”. IWA Publishing, USA. Murphy, J. D., McKeogh, E., Kiely G., (2004). “Technical/economical/environmental analysis of biogas utilization”. Apply Energy, 77,4, 407-427. Purcell, B. and Stentiford, E. (2001). Designing for large scale in-vessel composting. Pathogen in Biosolids and their Significance in Beneficial Use Programmes, Proceedings UKWIR/Aqua Enviro Pre-conference Workshop, 6th European Biosolids and Organic Residuals Conference, Aqua Enviro, Wakefield, Nov. 2001. Schulze, K.L. (1962). Continuous thermophilic composting. Appl. Microbiol., 10: 108–122. Sikora, L.J., Tester, C.F. and Hornick, S. (1980). Manual for Composting Sewage Sludge By the Beltsville Aerated–Pile Method. EPA- 600/8-80-022, USA, 65 pp. WHO International Reference Centre for Wastes Disposal (1978). Methods of Analysis of Sewage Solid Wastes and Compost. CH-8600, D bendorf, Switzerland. Willson, G.B., Parr, J.F., Epstein, E., Marsh, P.B., Chaney, R.L., Colacicco, D., Burge, W.D., Yongjie W., Yangsheng L., (2005). Effects of sewage sludge compost application on crops and cropland in a 3-year field study. Chemosphere 59 :1257–1265. Zaini U. and Mogens H., (2006)."Municipal wastewater management in developing countries”. IWA Publishing, USA. 13/13